Prior Art
It has been long recognized by engine builders and more particularly by specialists in high performance engines that control of valve timing will yield desired engine operation results. The ideal timing of intake and exhaust valves at idle conditions, at normal load range conditions and at high performance conditions is very different. Since valves are controlled by cams it is necessary to compromise the timing to suit a particular purpose. In production engines, valve timing is a compromise leaning towards the normal load or speed ranges to the detriment of the idle range and the high performance range. Likewise in high performance engines the timing is adjusted toward the high performance demands of the engine and therefore at the idle and normal load ranges valve timing is not optimal.
As early as 1903 Alexander Winton used a pneumatic device to vary valve lift. His particular intent at that time was throttling the engine with intake valves as opposed to throttling the engine with the conventional throttle plate. More recently there have been centrifugal cam sprockets which are capable of varying valve timing as a function of engine speed but not varying lift or duration of opening.
In addition there have been systems which completely disable the operation of the valves and therefore effectively close off one or more cylinders during different engine operating ranges. A recent commercial engine using this concept is Cadillac's 8-6-4 engine. In most of the known control systems the forces involved in opening and closing valves in the engine requires expensive and very high powered solenoids. This places a high cost penalty on the engine for the consumer.
U.S. Pat. No. 3,439,661 entitled "Control Displacement Hydraulic Lifter" by Weiler, teaches a hydraulic valve lifter. U.S. Pat. No. 4,112,884 entitled "Valve Lifter for an Internal Combustion Engine" by Tominaga, teaches a valve lifter design. Both patents operate to provide some timing control to the valves. U.S. Pat. No. 4,111,165 entitled "Valve Operating Mechanism of an Internal Combustion Engine" by Aoyama et al, teaches control of the oil in a hydraulic valve lifter in response to engine speed and throttle opening to spill the oil during deceleration thereby limiting the traveling of the valve lifter. U.S. Pat. No. 4,258,671 entitled "Variable Lift Mechanism used in Internal Combustion Engine" by Takizawa et al, teaches electromagnetic valve control of hydraulic valve lifters in an overhead cam (OHC) engine. In response to engine temperatures, manifold pressure and speed, the oil pressure in the lifter is adjusted to form the solid link necessary to operate the engine valve. This particular patent ('671) teaches the control of all cylinders. Each of the last two patents ('165 and '671) does not teach driving the oil back into the lifter for restoring the valve lifter to a normal start position after each operation in order that each engine cycle is independently controlled. Therefore, in the next engine cycle the electronic control unit controlling the operation of the oil does not know the location of the lifter. If the next engine cycle requires a later valve opening, the valve opening will not change from the previous engine cycle inasmuch as the lifter has not been re-extended. Aoyama et al shows a pump and a regulator to supply oil pressure to the lifter and Takizawa et al teaches an oil supply gallery fed by an oil supply which is driven by the engine. Without more, the normal engine oil pressures are inadequate to return a collapsed lifter to its full height in the available time between engine cycles. In both systems, the addition of a boost pressure pump of adequate pressure capacity is both expensive and adds an unnecessary load on the engine, therefore defeating the purposes and the advantages gained by controlling the valves of an engine.
To solve the above problems, there is disclosed herein an engine valve timing control system using the engine oil supply to operate the hydraulic valve lifters or adjusters. By controlling the fluid pressures pulses developed within the oil supply as a result of lifter operation, very high pulsed pressures are directed to the various lifters to assist in returning or re-extending the lifters to their normal position between engine cycles. The system is a microprocessor based control system wherein various engine sensors sense the engine conditions and the microprocessor in response to the sensed engine conditions addresses a memory unit containing a map of engine conditions versus valve opening times. From the memory unit a signal is supplied to a particular timer unit for a given cylinder. The timer, operating in conjunction with a known position of the piston in the cylinder will operate electrohydraulic solenoid valves for directing and maintaining a predetermined amount of oil in an associated hydraulic lifter.
These and other advantages will be found in the following detailed description and drawings.